Optimizing oxidized coal flotation through pH adjustment and inorganic salt ion

The effect of pH on zeta potential, combustible matter recovery, and Fourier transform infrared (FTIR) spectrum of oxidized coal was studied, and also the effects of Na+, Mg2+, and Fe3+ on oxidized coal flotation at different pH were investigated. The optimal floatability of oxidized coal was explored through the conditions of pH and inorganic salt ion. Both combustible matter recovery and zeta potential decreased as pH increased. The maximum combustible matter recovery and approximate isoelectric points (IEP) were obtained at pH 3. The adsorption peaks of oxygen-containing functional groups and hydrophobic groups in FTIR spectrums were, respectively, lowered and enhanced while pH varied from 7 to 3. Oxidized coal flotation was improved by Na+, Mg2+, and Fe3+ in acidic condition but depressed in alkaline condition. Compared with the combustible matter recovery in the absence of inorganic salt ion, Na+ presented the maximum increase rate of combustible matter recovery at pH 6 but also the minimum at pH 12. The combustible matter recovery for Na+ gradually increased while that for Mg2+ and Fe3+ generally decreased with the increase in ion concentration. The optimal floatability was gained at pH 3 and in the presence of Na+ with a concentration of 1600 g/t.